1. Field of the Invention
The invention relates to a magnetoresistive sensor, typically used in a magnetic disk drive; and, more specifically, the invention relates to a magnetoresistive sensor having bias magnets with substantially vertical endwalls.
2. Description of the Background Art
Disk drives using magnetic recording of digital information store most of the data in contemporary computer systems. A disk drive has at least one rotating disk with discrete concentric tracks of data. Each disk drive also has at least one recording head typically having a separate write element and read element for writing and reading the data on the tracks.
The read element in most contemporary disk drives includes a magnetoresistive spin valve sensor. A magnetic spin valve sensor includes a sandwich of layers, also known as a sensor stack, including a ferromagnetic pinned layer, a nonmagnetic electrically conducting layer, and a ferromagnetic free layer. The sensor stack is disposed between two magnetic shields. The distance between the two magnetic shields determines the read gap. The size of the read gap strongly influences the capability of the sensor to accommodate high recorded density. The resistance of the spin valve sensor changes with respect to the direction and magnitude of an applied magnetic field such as the field from a written magnetic transition on a disk. To detect the change in resistance, sense current is passed through the sensor through electrical leads. The electrical leads are also known as lead layers, or more simply, leads. Typically, hard bias material is disposed in layers near the ends of a sensor stack forming permanent magnets which impose a stabilizing magnetic biasing field on the sensor stack. The permanent magnets are also known as hard bias magnets or bias magnets.
The disposition and placement of the bias magnets is important for the performance of the spin valve sensor. In a typical prior art spin valve, the sensor stack is formed using a photoresist liftoff structure which leaves rounded or sloped ends to the sensor stack. The hard bias material is then deposited over these sloped ends forming abutted junctions. Each abutted junction has a significant width resulting in a relatively broad distribution of the magnetic pole at each abutted junction. As the required trackwidths of spin valve sensors become more and more narrow, the width of the abutted junction becomes a much greater fraction of the total trackwidth. In addition, the abutted slopped junction is somewhat inefficient requiring a rather thick layer of hard bias material to fully stabilize the sensor. The deleterious effects associated with abutted junctions are becoming more troublesome as the required trackwidths become smaller.
Accordingly, what is needed is a magnetic spin valve sensor in which the hard bias material forms a narrow and more effective junction with the sensor stack.